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2 Adeniyi Mojisola Oluwayemisi

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Simulating the influence of doubled CO2 on the water budget over West Africa using RegCM4.7

Adeniyi Mojisola Oluwayemisi

Meteorology Hydrology and Water Management. Research and Operational Applications

2020

Vol. 8, Iss. 2

12--19

This paper simulates the responses of water budget components to doubled CO2 (2 × 378 ppm) concentration in the atmosphere with atmospheric and oceanic surface warming of 2°C. Simulations employed version 4.7 of the Regional Climate Model of the International Centre for Theoretical Physics (ICTP). Two six-year experiments were each repeated twice with the same model physics and parameterizations. The control experiment held the CO2 concentration at 378 ppm (no warming), while the other experiment specified doubled CO2 concentration and warming. The results showed a positive response (60-100% increase) to doubled CO2 for precipitation, runoff, and storage terms in Sierra Leone, Burkina Faso, Guinea Bissau, and the ocean area between 3 and 13°N. However, there was a negative response (up to 60%) for northern Senegal, southern Mali, and northern Nigeria. The reductions in water fluxes were observed mostly on the leeward side of the highlands. Evapotranspiration showed a negative response (1-20%) to doubled CO2 on the land north of 20°N. Burkina Faso and southern Mali responded oppositely to doubled CO2, despite their spatial proximity.

Sensitivities of the Tiedtke and Kain-Fritsch Convection Schemes for RegCM4.5 over West Africa

Adeniyi Mojisola Oluwayemisi

Meteorology Hydrology and Water Management. Research and Operational Applications

2019

Vol. 7, Iss. 2

27--37

Realistic simulation of weather and climate parameters over West Africa is daunting, so the performance of the Tiedtke and Kain-Fritsch convection schemes within version 4.5 of the Regional Climate Model (RegCM4.5) of the International Centre for Theoretical Physics, Trieste is evaluated over West Africa for improved simulation. The two schemes are compared to two traditional mixture schemes (Grell on land and Emanuel on Ocean), outperforming the mixture schemes with reduced magnitude and spatial coverage of dry bias. Both schemes simulate precipitation over West Africa with a low dry bias, however, the Kain-Fritsch convection scheme simulates more realistic precipitation in the West African convective environment. This is associated with the inclusion of a variable cloud radius and the convective available potential energy closure for the Kain-Fritsch in contrast to a fixed cloud radius and moisture convergence of the of the Tiedtke scheme. The simulated outgoing longwave radiation and omega lend support to the spatial variations and amount of simulated precipitation in the different areas by the schemes. The spatial variation of simulated temperature over the target region shows lower bias than precipitation by all the convection schemes. Soil moisture is more accurately simulated (correlation coefficient ~1) in the savannah (8-10°N) and Sahel (22-28°N) environments by all the convection schemes. Tiedtke performs the most accurate simulations of the pattern and profile of zonal wind which controls climate circulation, with slightly weaker simulations of the Africa easterly jet with core magnitude less than 10 m·s-1. The accuracy of the KF and Tiedtke in RegCM4.5 in simulating the climate of West Africa is documented for the first time for application in future studies over the region.